quantity vs abstract entity

quantity and abstract entity both are nouns.

Word	Noun	Adjective	Verb	Adverb
quantity	Yes	No	No	No
abstract entity	Yes	No	No	No

As nouns, abstract entity is a hypernym of quantity; that is, abstract entity is a word with a broader meaning than quantity:

quantity: how much there is or how many there are of something that you can quantify
abstract entity: a general concept formed by extracting common features from specific examples

Other hypernyms of quantity include abstraction.

quantity (noun)	abstract entity (noun)
how much there is or how many there are of something that you can quantify	a general concept formed by extracting common features from specific examples
an adequate or large amount
the concept that something has a magnitude and can be represented in mathematical expressions by a constant or a variable